MATL, 12 bytes
q&=sqt&=tsvv
The input is a string enclosed in single quotes. Single quotes in the string are escaped by duplicating.
The output is a non-empty matrix, which is truthy if it doesn't contains zeros, and is falsy if it contains at least a zero.
Try it online! Or verify all test cases, including the standard truthiness/falsiness test for convenience.
How it works
Statements marked with (*)(*)
are neither necessary nor harmful, and have been included only to make the string contining the source code non-discriminating.
q % Implicit input. Convert chars to code points and subtract 1 from each (*)
&= % Square matrix of all pairwise equality comparisons
s % Sum of each column. Gives a row vector
q % Subtract 1 from each value. An entry equal to 0 indicates the input string
% is discriminating because some character appears only once
t % Duplicate
&= % Square matrix of all pairwise equality comparisons. An entry equal to 0
% indicates the input string is discriminating because some character is
% more repeated than some other
t % Duplicate (*)
s % Sum of each column (*) (all those sums will be positive if the previous
% matrix doesn't contain zeros)
v % Vertically concatenate the matrix and the vector of its column sums
v % Vertically concatenate the resulting matrix with nothing (*)
% Implicit display